High linear density, high modulus, high tenacity yarns and methods for making the yarns

ABSTRACT

The present invention relates to a yarn, comprising (a) a plurality of fibers having an orientation angle of no more than 8.0 degrees and made of a para-aramid, (b) a linear density of at least 2666 dtex (2400 denier), (c) a modulus of at least 810 grams per dtex (900 grams per denier), and (d) a tenacity of at least 18 grams per dtex (20 grams per denier). The invention further relates to methods of making such yarn.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to high linear density, high modulus, hightenacity yarns and methods of making the yarns.

2. Description of Related Art

Para-aramid yarns have been long known for their light weight, highdenier, high strength and high modulus. They have been used in a greatnumber of applications requiring various combinations of para-aramidyarn properties. There is a strong demand and need for yarns havingstill higher denier, modulus and/or tenacity combinations for use instill more demanding applications.

U.S. Pat. No. 5,001,219 discloses high modulus, high tenacitypara-aramid yarns and a process for making the yarns. However, it doesnot disclose how to make para-aramid yarns with a linear density of atleast 2666 dtex and a modulus of at least 810 grams per dtex whilemaintaining tenacity of at least 18 grams per dtex.

It is an objective of this invention to provide a high denier yarn witha high modulus and a high tenacity capable of being used in moredemanding applications than prior art yarns.

It is a further objective to make the yarn in an on-line commercial yarnmanufacturing process.

These and other objects of the invention will be clear from thefollowing description.

BRIEF SUMMARY OF THE INVENTION

The invention relates to a yarn, comprising: (a) a plurality of fibershaving an orientation angle of no more than 8.0 degrees and made ofpara-aramid, b) a linear density of at least 2666 dtex (2400 denier),(c) a modulus of at least 810 grams per dtex (900 grams per denier), and(d) a tenacity of at least 18 grams per dtex (20 grams per denier).

The invention further relates to a continuous process for making apara-aramid yarn having a linear density of at least 2666 dtex (2400denier), a modulus of at least 810 grams per dtex (900 grams per denier)and a tenacity of at least 18 grams per dtex (20 grams per denier),comprising:

extruding an anisotropic solution of para-aramid in a solvent-through aspinneret having a plurality of holes forming a plurality of fibers,

passing the fibers through a gas and then a coagulating liquid,

combining the fibers into a yarn,

washing the yarn with a washing solution,

removing some of the washing solution from the surface of the yarn,

treating the yarn by heating the yarn from 120° C. to 260° C. under atension of 0.90 to 2.25 grams per dtex (1.00 to 2.50 grams per denier)for a first heating time of 1.6 to 6.0 seconds, and

after the first treating step, treating the heated yarn from 300° C. to400° C. under a tension of 2.25 to 4.50 grams per dtex (2.50 to 5.00grams per denier) for a second heating time of 0.2 to 5.0 seconds,

cooling the yarn to a temperature of 125 to 170° C.,

applying a finish on the yarn, and

winding the yarn on a spool for the first time in the process.

BRIEF DESCRIPTION OF THE DRAWING(S)

The invention can be more fully understood from the following detaileddescription thereof in connection with accompanying drawings describedas follows.

FIG. 1 illustrates apparatus for performing initial steps of acontinuous yarn manufacturing process in accordance with the presentinvention.

FIG. 2 illustrates a first embodiment of apparatus for performing finalsteps of the continuous yarn manufacturing process in accordance withthe present invention.

FIG. 3 illustrates a second embodiment of apparatus for performing finalsteps of the continuous yarn manufacturing process in accordance withthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention is directed to high linear density, high modulus, hightenacity yarns and processes for making such yarns.

Fiber and Yarn

Yarns of the present invention comprise (a) a plurality of fibers havingan orientation angle of no more than 8.0 degrees and made of para-aramidhaving an inherent viscosity of 5.2 to 6.2 dl/g, (b) a linear density ofat least 2666 dtex (2400 denier), (c) a modulus of at least 810 gramsper dtex (900 grams per denier), and (d) a tenacity of at least 18 gramsper dtex (20 grams per denier).

For purposes herein, the term “fiber” is defined as a relativelyflexible, macroscopically homogeneous body having a high ratio of lengthto width across its cross-sectional area perpendicular to its length.The fiber cross section can be any shape, but is typically circular.Herein, the term “filament” is used interchangeably with the term“fiber”.

The fibers can be any length. The fibers can be continuous filamentswhich are filaments that extend typically for a meter or much longer.Filaments are spun in a continuous form frequently as part of amultifilament yarn, wound unto a spool and then cut after the desiredamount is placed on the spool. The filaments can be cut into staplefibers having a length of about 0.25 to about 5 inches (about 0.64 cm toabout 12.7 cm). The staple fiber can be straight (i.e., non crimped) orcrimped to have a saw tooth shaped crimp along its length, with a crimp(or repeating bend) frequency of about 3.5 to about 18 crimps per inch(about 1.4 to about 7.1 crimps per cm).

The fibers have an orientation angle of no more than 8.0 degrees.Preferably, the fibers have an orientation angle of 5.0 to 8.0 degrees.More preferably, the fibers have an orientation angle of 6.0 to 8.0degrees. Even more preferably, the fibers have an orientation angle of7.0 to 8.0 degrees.

Preferably, the fibers have an apparent crystallite size at the 110intensity peak of 70 to 85 Angstroms. More preferably, the fibers havean apparent crystallite size at the 110 intensity peak of 71 to 78Angstroms.

Preferably, the fibers have an apparent crystallite size at the 200intensity peak of 54 to 60 Angstroms. More preferably, the fibers havean apparent crystallite size at the 200 intensity peak of 54 to 59Angstroms.

Preferably, the difference between the apparent crystallite size at the110 intensity peak and the apparent crystallite size at the 200intensity peak is at least 15 Angstroms. More preferably, the differenceis from 15 to 25 Angstroms.

In one embodiment, the fibers have a crystal perfection index of 55 to70 percent. Preferably, the fibers have a crystal perfection index of 55to 65 percent.

In one embodiment, the fibers have a linear density of 1.10 to 2.50 dtex(1.00 to 2.25 denier). Preferably, the fibers have a linear density of1.10 to 1.67 dtex (1.00 to 1.50 denier). More preferably, the fibershave a linear density of 1.33 to 1.55 dtex (1.20 to 1.40 denier).

The yarns are made of a plurality of the filaments. The filaments inyarns can be substantially parallel in which case the yarns are calledtows or the filaments can be intermingled or entangled along the lengthof the yarn to maintain the unity of the yarn. Yarns can be made bycombining two or more sets of fibers or tows. When two or more tows areinvolved, they can be entangled by an air jet to make them a holdtogether as a unitary yarn.

The yarn preferably comprises 1100 to 2500 fibers, more preferably 1900to 2500 fibers and even more preferably 2000 to 2350 fibers.

The yarn has a “high” linear density which for purposes of thisinvention is defined as a linear density of at least 2666 dtex (2400denier). The yarn can have a linear density of as much as 3444 dtex(3100 denier) or more. Preferably, the yarn has a linear density of 2777to 3444 dtex (2500 to 3100 denier). More preferably, the yarn has alinear density of 3000 to 3222 dtex (2700 to 2900 denier).

The yarn has a “high” modulus which for purposes of this invention isdefined as a modulus of at least 810 grams per dtex (900 grams perdenier). The yarn can have a modulus of as much as 990 grams per dtex(1100 grams per denier) or more. Preferably, the modulus is from 810 to990 grams per dtex (900 to 1100 grams per denier). More preferably, themodulus is from 846 to 945 grams per dtex (940 to 1050 grams perdenier).

The yarn has a “high” tenacity which for purposes of this invention isdefined as a tenacity of at least 18 grams per dtex (20 grams perdenier). The yarn can have a tenacity of as much as 24.3 grams per dtex(27.0 grams per denier) or more. Preferably, the tenacity is from 18.0to 24.3 grams per dtex (20.0 to 27.0 grams per denier). More preferably,the tenacity is from 19.8 to 23.4 grams per dtex (22.0 to 26.0 grams perdenier).

Polymer

The yarns of the present invention are made of para-aramid having aninherent viscosity of 5.2 to 6.2 dl/g, and preferably an inherentviscosity of 5.4 to 6.0 dl/g.

By the term “para-aramid” is meant the homopolymer resulting frommole-for-mole polymerization of p-phenylene diamine and terephthaloylchloride and, also, copolymers resulting from incorporation of smallamounts of other diamines with the p-phenylene diamine and of smallamounts of other diacid chlorides with the terephthaloyl chloride. As ageneral rule, other diamines and other diacid chlorides can be used inamounts up to as much as about 10 mole percent of the p-phenylenediamine or the terephthaloyl chloride, or perhaps slightly higher,provided only that the other diamines and diacid chlorides have noreactive groups which interfere with the polymerization reaction.Para-aramid, also, means copolymers resulting from incorporation ofother aromatic diamines and other aromatic diacid chlorides such as, forexample, 2,6-naphthaloyl chloride or chloro- or dichloroterephthaloylchloride; provided, only that the other aromatic diamines and aromaticdiacid chlorides be present in amounts which do not adversely affect theproperties of the para-aramid. The preferred para-aramid ispoly(p-phenylene terephthalamide) homopolymer (PPD-T).

Additives can be used with the para-aramid in the fibers and it has beenfound that up to as much as 10 percent, by weight, of other polymericmaterial can be blended with the aramid or that copolymers can be usedhaving as much as 10 percent of other diamine substituted for thediamine of the aramid or as much as 10 percent of other diacid chloridesubstituted for the diacid chloride of the aramid.

Suitable aramid fibers are described in Man-Made Fibers—Science andTechnology, Volume 2, Section titled Fiber-Forming Aromatic Polyamides,page 297, W. Black et al., Interscience Publishers, 1968. Aramid fibersare, also, disclosed in U.S. Pat. Nos. 4,172,938; 3,869,429; 3,819,587;3,673,143; 3,354,127; and 3,094,511.

Process for Making the Yarn

If not already prepared, a first step can be preparing an anisotropicdope or spinning solution comprising dissolving the para-aramid polymerin a solvent. Suitable solvents include strong acids, such as, sulfuricacid, chloro and fluoro sulfonic acids, nitric acid, hydrogen chlorideor hydrofluoric acid.

The dope solution should contain a high enough concentration of polymerfor the polymer to form an acceptable filament after extrusion andcoagulation. The concentration of the para-aramid polymer is preferablyat least about 14 weight percent, more preferably at least about 15weight percent and most preferably at least about 19 weight percent. Themaximum concentration is limited primarily by practical factors, such aspolymer solubility and dope viscosity. The concentration of polymer ispreferably no more than 21 weight percent, and more preferably no morethan about 20.5 weight percent.

The polymer dope solution can contain additives such as anti-oxidants,lubricants, ultra-violet screening agents, colorants and the like whichare commonly incorporated.

Referring to FIG. 1, the process for making the yarn includes a step ofextruding the anisotropic dope solution of the para-aramid polymer in asolvent through a spinneret 2 having a plurality of holes forming aplurality of dope fibers or filaments 4. The polymer anisotropic dopesolution is forced from a source 6, though a distribution network 8,such as, by meter pumps 10, through temperature regulating devices 12,through the dies or spinnerets 2 to extrude, spin or make the dopefilaments 4. Preferably, the temperature regulating devices 12 controlthe temperature of the dope solution to be about 65 to 85° C. as itexits the spinnerets 2. Each spinneret 2 contains a plurality of holes.In one embodiment, the spinnerets 2 can contain 600 to 1500 holes, andthey may be arranged in circles, grids, or in any other desiredarrangement. The spinnerets 2 can be constructed out of ordinarymaterials that will not be degraded by the dope solution, such asstainless steel.

Dope solution exiting the spinnerets 2 form the dope filaments 4 thatenter a gap 14 between the spinneret 2 and a coagulation bath 16. Thegap 14 is typically called an “air gap” although it need not containair. The gap 14 may contain any gas that does not induce coagulation orreact adversely with the dope, such as air, nitrogen, argon, helium orcarbon dioxide. The dope filaments 4 are passed or drawn across orthough the air gap 14, with or without stretching. The draw should besufficient to provide a filament having the desired diameter.

The process includes passing the dope filaments 4 though the gas gap 14and then through the coagulating liquid in the bath 16. The filaments 4are “coagulated” by passing them through the coagulation bath 16containing a liquid such as water or a mixture of water and the solvent,e.g., sulfuric acid, which removes enough of the solvent to preventsubstantial stretching of the filaments 4 during any subsequentprocessing.

The term “coagulation” as used herein does not necessarily imply thateach dope filament 4 is a flowing liquid and changes into a solid phasein the coagulation bath 16. The dope filament 4 can be at a temperaturelow enough so that it is essentially non-flowing before entering thecoagulation bath 16. However, the coagulation bath 16 does ensure orcomplete the coagulation of the filament, i.e., the conversion of thepolymer from a dope solution to a substantially solid polymer filament.The amount of solvent removed when the filaments are passed through thecoagulation bath 16 will depend on the residence time of the filaments 4in the coagulation bath 16, the temperature of the bath 16, and theconcentration of solvent therein.

The temperature of the coagulation bath 16 is preferably at least about3° C., more preferably at least 10° C., and is preferably no greaterthan 30° C., and more preferably no greater than 20° C. The residencetime of the filaments 4 in the coagulation bath 16 is preferably atleast 0.015 second, and is preferably no more than 0.100 second. Theconcentration of acid in the coagulation bath 16 is preferably at least3 percent by weight, more preferably at least 6 percent, and ispreferably no greater than 15 percent and more preferably no greaterthan 10 percent.

U.S. Pat. Nos. 3,869,429, 4,298,565, 4,340,559 disclose spinning andcoagulating structures that are suitable for use in the presentinvention.

The process includes combining multiple fibers 4 into a multifilamentyarn 18 before, during or preferably after passing the filaments 4through the coagulation bath 16.

Then the process includes washing the coagulated filaments ormultifilament yarn 18 with a wash solution in one or more wash step toremove more and most of the solvent from the yarn 18. The washing of theyarn 18 can be carried out by running the yarn 18 through a series ofbaths and/or through one or more washing cabinets. FIG. 1 depicts onewashing bath or cabinet 20. Washing cabinets typically comprise anenclosed cabinet 20 containing a pair of rolls 22 which the filamentstravel around a number of times prior to exiting the cabinet 20. As theyarn 18 travels around the rolls 22, it is sprayed with a washingsolution. The washing solution is continuously collected in the bottomof the cabinet 22 and drained therefrom.

The yarn 18 is directed by change of direction rolls 24 and driven bymotorized feed rolls 26 to pass the yarn 18 from the coagulation bath 16to the wash cabinet 20.

The temperature of the washing solution is preferably at least 15° C.,more preferably at least 50° C., and is preferably no greater than 120°C. and more preferably no greater than 100° C. The washing solution mayalso be applied in vapor form (steam), but is more conveniently used inliquid form. The residence time of the yarn 18 in the washing bath(s) orcabinet(s) 20 will depend on the desired concentration of residualsolvent in the filaments or yarn 18, but typical residence times are inthe range of from about 2 seconds to about 20 seconds.

Preferably, the surface of the filaments or yarn 18 is not allowed todry after passing through the coagulation bath 16 and before the washingstep(s) are completed. It is theorized, without intending to be bound,that the wet, “never-dried” surface of the filaments or yarn 18 isrelatively porous and provides paths to wash residual solvent frominside the filaments or yarn 18. On the other hand, it is theorized thatpores inside the filaments close when they become dry and do not openeven when they become wet again. The closed pores, it is believed, trapresidual solvent inside the filaments or yarn 18.

The washing step of the present invention can additionally includecontacting the coagulated yarn 18 with a neutralization solution (suchas in a bath or cabinet 28) containing water and an effective amount ofa base under conditions sufficient to neutralize sufficient quantitiesof the solvent in the yarn 18 to a salt of the base and the acid.Suitable bases that can be used include NaOH, KOH, Ca(OH)2, Mg(OH)2,Sr(OH)2, Na2CO3, NaHCO3, K2CO3, KHCO3, CaCO3, Ca(HCO₃)2, CaO,trimethylamine, triethylamine, triethylenediamine, tributylamine,pyridine, or mixtures thereof. Preferably, the base is water soluble.FIG. 1 depicts cabinet 28 containing a pair of rolls 30 which thefilaments travel around a number of times prior to exiting the cabinet28. As the yarn 18 travels around the rolls 30, it is sprayed with aneutralizing solution.

After contacting the yarn 18 with the neutralization solution, thewashing step optionally includes the step of contacting the yarn with awashing solution containing water to remove all or substantially allexcess base. This washing solution can be sprayed on in the washing bathor cabinet 28 or another washing bath or cabinet.

Then the process includes removing or stripping some of the washingsolution from the surface or exterior of the yarn 18, such as, by adewaterer device 32. The dewaterer can be a device that emits a jet ofhigh velocity air directed at the yarn, or a mechanical water strippercomprising a series of polished ceramic pins arranged such that the pinspress lightly against the yarn, to remove excess water. The excess wateris generally water on the surface of the yarn. After thisremoving/stripping step, the moisture content of the yarn 18 istypically no more than about 85 wt % moisture based on the dried yarn.

Then the process includes a first treating step which comprises heatingthe yarn under tension for a first total heating time. This can beaccomplished in one or a plurality of sequential steps.

In the first treating step, the yarn 18 can be heated by a firstplurality of steam heated hot rolls 34. The steam heated hot rolls 34treat the yarn 18 by heating the yarn from 120° C. to 220° C. under atension of 0.90 to 2.25 grams per dtex (1.00 to 2.50 grams per denier)for a heating time of 1.6 to 5.5 seconds. Preferably, in this firsttreating step, the yarn is heated from 150° C. to 200° C. under atension of 0.9 to 2.0 grams per dtex for a heating time of 2.0 to 5.0seconds. More preferably, in this first treating step, the yarn isheated from 170° C. to 180° C. under a tension of 0.9 to 1.5 grams perdtex for a heating time of 2.5 to 4.0 seconds. The time that the yarncontacts the hot rolls 34 is the heating time. In one embodiment, thefirst plurality of hot rolls 34 includes at least two steam heated rolls34 and the yarn contacts the at least two steam heated rolls 34 toremove most of the wash solution from the yarn 18. After exiting thesesteam heated rolls 34, the yarn typically has a moisture content of nomore than 50 wt % moisture content, preferably no more than 40 wt % andmore preferably from 20 wt % to 40 wt % moisture content.

This first treatment step stretches the yarn 18 under relatively lowtension. This is accomplished by keeping the yarn moisture contentrelatively high. This reduces the damage to filaments. It is believedthat in this step the water in the fibers facilitate the properalignment of the molecules thereby increasing the modulus of thefilaments.

In the first treating step, the yarn can optionally be additionallyheated by a second plurality of electrically heated hot rolls 36. FIG. 2illustrates a process where the second plurality of rolls 36 comprisessix rolls 41-46. The yarn 18 contacts the at least two steam heatedrolls 34 before the yarn 18 contacts the first plurality of electricallyheated rolls 36. The electrically heated hot rolls 36 treat the yarn 18by heating the yarn from 120° C. to 260° C. under a tension of 0.90 to2.25 grams per dtex (1.00 to 2.50 grams per denier) for a heating timeof 0.20 to 0.50 seconds, preferably 0.25 to 0.45 seconds. The rolls 36can be heated at increasing temperatures from roll 41 to roll 46 oralternatively, the last roll 46 (or the last several rolls) can beheated at progressively higher temperatures to approach the temperatureof the next roll in the next or second treatment stage.

The total time that the yarn is treated in the first treating step isthe sum of the heating time by contact with the steam heated hot rolls34 plus the heating time by contact with the electrically heated hotrolls 36. Thus, the total heating time in the first treating step can befrom 1.6 seconds to 6.0 seconds. Alternatively, for illustrationpurposes, the total lowest treating duration in the first treating stepcan be 1.8 seconds, 2.0 seconds, 2.2 seconds, 2.5 seconds, or 2.7seconds. Also alternatively, for illustration purposes, the totalhighest treating duration in the first step can be 5.5 seconds, 5.0seconds, 4.5 seconds or 4.0 seconds.

The yarn exiting the first plurality of steam heated hot rolls 34 or thefirst plurality of electrically heated rolls 36 has a yarn moisturecontent of no more than 50 wt % moisture content, preferably no morethan 40 wt % and more preferably from 20 wt % to 40 wt %.

Then the process includes a second treating step of treating the yarn byheating it from 300° C. to 400° C. under a tension of 2.25 to 4.50 gramsper dtex (2.50 to 5.00 grams per denier) for a heating time of 0.2 to5.0 seconds resulting in the high linear density, high modulus, hightenacity yarn. Preferably, in this second treating step, the yarn isheated from 340° C. to 380° C. under a tension of 2.7 to 4.5 grams perdtex (3.0 to 5.0 grams per denier) for a heating time of 0.2 to 4.0seconds. More preferably, in this second treating step, the yarn isheated from 350° C. to 400° C. under a tension of 2.7 to 4.5 grams perdtex (3.0 to 5.0 grams per denier) for a heating time of 0.3 to 1.0seconds.

In the second treating step, the yarn can be heated by a secondplurality of hot rolls 48. When the yarn 18 is heated by passing thefibers over the second plurality of hot rolls 48, the time the yarn 18contacts the rolls 48 is the heating time for the second treatment step.In one embodiment, the second plurality of hot rolls 48 comprises eightrolls 51-58 which are electrically heated. The hot rolls 48 do not allhave to be heated at the same temperature as long as they are eachheated in the specified temperature range.

In the second treatment step, the yarn 18 is heated at a highertemperature to remove moisture content and to crystallize or fix thealigned molecules in place locking the high modulus in the yarn.

In other embodiments, as illustrated in FIG. 3, the yarn 18 can beheated in one or more dryer 60, such as a convention oven, or in one ormore section of a dryer that has separate temperature controls, ratherthan by steam heated rolls 34 and/or rather than by the electricallyheated rolls 36, 48. The temperature in the dryer(s) and the dryerresidence time is set to provide the same or substantially the same heatand tension treatment to the yarn as specified above. The dryer can beprovided with a nitrogen or other non-reactive atmosphere.

Then the process includes a step of cooling the yarn 18 to a temperatureof 125 to 170° C. In one embodiment, the yarn is cooled by passing theyarn 18 over a fourth plurality of rolls 62 heated at 125 to 170° C. andthe time the yarn contacts the rolls 62 is 0.2 to 4.0 seconds. Thefourth plurality of rolls 62 can be steam or electrically heated. Theycan be positioned in one or more cabinet 64. This cooling step can alsobe done in an oven, rather than by contacting rolls 62.

Then the process includes a step of applying a finish on the yarn 18.FIGS. 2 and 3 show a finish applicator 66 for this purpose. This stepfurther includes the optional application of water, such as, by a waterapplicator 68 on the yarn 18 thereby increasing the moisture contentpreferably to no more than 12 wt % moisture content and more preferablyfrom 4 to 8 wt % moisture content. A purpose of the cooling step is sothat the yarn 18 is at a low enough temperature so as not to burn off orharm the finish (including the water) applied to the yarn. The finishcan be a lubricant, an emulsifier, water or mixtures thereof. Suitablelubricants include mineral oils, vegetable oils (e.g., triglycerides),and fatty acid esters (e.g., coconut oil, castor oil, polyethyleneglycol, etc.). Suitable emulsifiers include fatty acid soaps, fattyamines and glycols. U.S. Pat. Nos. 5,478,648 and 5,674,615 and Europeanpatent 0 423 703 A2 disclose suitable finishes for aramid fibers. Thefinishes are selected to facilitate subsequent processing and use of theyarns.

The process ends by winding the yarn 18 on a spool 70 to form a packagefor the first time in the process. In this regard, the yarnmanufacturing process is a “continuous” process. The yarn 18 stayson-line and continuously moves from formation through the washing step,the removing step, the first and second treating steps, the coolingstep, and the applying step before the yarn 18 is wound onto a spool 70.The yarn 18 is not wound up or otherwise taken “off line” for processingelsewhere and then brought back and unwound in order to perform any ofthe processing steps of the invention.

Rolls (including motorized devices) 72 are suitably positioned totransport the yarn through the process.

INDUSTRIAL APPLICABILITY

High denier, high modulus, high tenacity yarns in accordance with thepresent invention have many uses. They are particularly useful asreinforcement of fiber optic cables. They are also very useful in oiland gas exploration and processing, in mass transportation applicationsand in building and construction applications.

Test Methods

The following test methods represent descriptions of methods that can beused to measure parameters used throughout this disclosure and were usedin the following Examples.

Temperature is measured in degrees Celsius (° C.).

Linear Density can be expressed as denier which is calculated as theweight of a 9000 meter sample in grams. Denier times (10/9) is equal todecitex (dtex). The yarn linear density was measured by weighing apremeasured length of yarn on a Vibroskop 400 Lenzing Instrumentobtained from W. Fritzmezger, Inc., of Spartanburg, S.C. 29302 using theASTM D1907 test method. The filament linear density was determined usingthe Vibroskop 400 using the ASTM 1577 test method.

Tenacity was determined in accordance with ASTM D 7269 and is themaximum or breaking stress of a fiber as expressed as force per unitcross-sectional area. The tenacity was measured on an Instron model 1130available from Instron Engineering Corp. of Canton, Mass. and isreported as grams per denier (grams per dtex).

Denier and tenacity tests performed on samples of fibers are at standardtemperature and relative humidity conditions prescribed by ASTMmethodology. Specifically, standard conditions mean a temperature of75+/−2° F. (21+/−1° C.) and relative humidity of 55%+/−2%.

Elongation (breaking elongation) was determined in accordance with ASTMD 7269 and is the strain in the sample when it ruptures. The elongationwas measured on an Instron model 1130 available from Instron EngineeringCorp. of Canton, Mass. and is reported as percent (%).

Modulus was determined in accordance with ASTM D 7269 and is the slopeof the tangent line to the initial straight line portion of the stressstrain curve, multiplied by 100 and divided by the adhesive-free denier.The modulus is generally recorded at less than 2% strain. The modulus ismeasured on an Instron model 1130 available from Instron EngineeringCorp. of Canton, Mass. and is reported as grams per denier (grams perdtex).

Inherent Viscosity (IV) is defined by the equation:

IV=ln(ηrel)/c

where c is the concentration (0.5 gram of polymer in 100 ml of solvent)of the polymer solution and ηrel (relative viscosity) is the ratiobetween the flow times of the polymer solution and the solvent asmeasured at 30° C. in a capillary viscometer. The inherent viscosityvalues reported and specified herein were determined using concentratedsulfuric acid (96% H₂SO₄).

Yarn Moisture is the amount of moisture included in a test yarndetermined by removing any finish (such as by washing) and then drying aweighed amount of wet yarn at 160° C. for 1 hour and then dividing theweight of the water removed by the weight of the dry yarn andmultiplying by 100.

Crystal Orientation Angle was measured using a Phillips XRG 3100 x-raygenerator equipped with a copper x-ray tube. The unit operated at 30 KVand 30 mA. A nickel filter was used in front of a 76.2 mm lengthcollimator, which had a 500 micron inner diameter, thus giving a 500micron collimated beam at the sample position. Para-aramid fibers,oriented by hand, were held in a parallel aligned set of fibers by athin collodion coating and mounted at the sample position on agoniometer head. Radiation diffracted from the sample traveled to thedetector through a flightpath filled with helium. The flightpathconsisted of a conical metallic hollow chamber with apex towards thesample and base at the detector. The apex and base were covered by 1.25micron Mylar® film windows. A 5 mm beamstop was glued to the Mylar® filmwindow at the center of the detector at the base of the conical chamber.The sample to detector distance was 9 cm. The 2D wire detector was aHiStar model from Bruker having a sensitivity area of 107.8 mm×107.8 mm.Sensitivity and spatial calibrations were performed according tomanufacturer's specifications, and these calibrations were used in theapplication of respective corrections by the data collection software(SAXS for WNT version 3.3 from Bruker). Exposures were a minimum of 1hour. The resultant data consisted of an array of 1024×1024 pixelscontaining 16-bit data or better. The data was read into Matlab (version7.4.0) and routines, based on standard analysis methods, were used toanalyze the variation in intensity in the azimuthal direction about thebeam center. The orientation angle was derived from four intensity peaksor maximums (two centered about the scattering angle at the 110 MillerIndices and two centered about the scattering angle at the 200 MillerIndices). The full width at half height (FWHH) of each of the fourintensity peaks was determined and averaged resulting in the orientationangle reported in Table 4. The method used to measure the FWHH for eachpeak was to determine the baseline intensity level at the level of thebackground. This baseline is subtracted from the total intensity at thepeaks. The FWHH is then determined to be the difference of the twoscattering angles on both sides of the maximum peak at which theintensity is half the maximum. A substantially similar and suitableprocedure for determining orientation angle is described in “X-RayDiffraction Methods in Polymer Science” by Leroy E. Alexander, WileyInterscience (1969) Chapter 4, p. 264. Orientation angle is measured indegrees.

Crystal perfection index and apparent crystallite size were obtainedusing a Phillips x-ray diffractometer. A Phillips long fine focus copperx-ray tube, type PW2773, was powered by a Spellman high voltagegenerator, type DF 60N3, operating at 40 KV and 40 mA. A thetacompensating slit was used on the incident beam and a graphitemonochromator was used on the diffracted beam. The diffractometer wasautomated by the use of stepping motors and a microprocessor, and wasoperated in theta-2theta mode. The detector system comprised ascintillation detector and pulse height analysis discrimination.Para-aramid fibers were wrapped side by side on a sample holder tocover, in a single layer, an area of 12.7 mm×25.4 mm, with the longdimension of this area in the direction of the axis of the fibers. Theportion of the holder illuminated by the x-rays was made of quartzsingle crystal, which prevented production of parasitic diffraction fromthe holder itself. The wrapped fibers were run in reflection geometry,and were mounted on the instrument such that the fiber axis was normalto the axis of the diffractometer. The diffractometer was fitted with anautomatic sample changer. Diffraction pattern data were collected from 6to 36 degrees in scattering angle in steps of 0.1 degrees. The data werecollected for 15 seconds at each point. The data was read into Matlab(version 7.4.0) and routines, based on standard analysis methods, usedto derive the crystal perfection index and apparent crystallite size.The data provides an intensity versus scattering angle diffractionpattern consisting of the 110 intensity peak at 20 degrees scatteringangle, and the 200 intensity peak at 23 degrees scattering angle.

Crystal perfection index (CPI) was determined by routines in Matlabsoftware using the following formula:

CPI=(1−A/B)100

where A is the height of the maximum intensity at the 200 peak (minusthe background intensity) and B is the minimum intensity between themaximum intensities at the 110 peak and the 200 peak (minus thebackground intensity). Crystal perfection index is measured in percent.

Apparent crystallite size (ACS) is a measure of the size of the crystalsin the direction of the normal to a particular set of crystallographicplanes. This is an “apparent” size because it is affected by otherfactors besides crystallite size, for example crystal perfection. ACSwas determined by routines in Matlab software according to the Scherrerformula described in “X-Ray Diffraction Methods in Polymer Science” byLeroy E. Alexander, Wiley Interscience (1969) Chapter 4, p. 264.Apparent Crystallite Size is measured in Angstroms.

Examples

The following examples are given to illustrate the invention and shouldnot be interpreted as limiting it in any way. All parts and percentagesare by weight unless otherwise indicated. Examples prepared according tothe process or processes of the current invention are indicated bynumerical values. Control or Comparative Examples are indicated byletters.

Four comparison examples A, B, C and D, and two inventive examples 1 and2 illustrating the invention, were carried out.

In each comparison and inventive example, an anisotropic spinningsolution was prepared by dissolving poly-p-phenylene terethalamidehomopolymer in 100.1% sulfuric acid so as to produce a 19.5 wt percentsolution. The homopolymer had an inherent viscosity of 5.6 dl/g. Thespinning solution was extruded through two spinnerets at a spinningsolution temperature of 76° C. into an air gap (D1) followed by acoagulation bath of 7% aqueous sulfuric acid maintained at a coagulationbath temperature of 3° C. in which overflowing bath liquid passeddownwardly through an orifice along with the filaments. The spinneretshad a specified number spinning holes of 0.064 mm diameter. Thefilaments were in contact with the coagulating bath liquid for about0.025 seconds. The filaments were separated from the coagulating liquidand combined into a single tow bundle or yarn.

Then the yarn was forwarded at a first line speed into and through twowashing stages. In the first stage, water having a temperature of 30° C.was sprayed onto the yarns to remove most of the acid. In the secondstage, an aqueous solution of sodium hydroxide was sprayed onto theyarns. The yarn was washed by first spraying strong-sodium hydroxidewater solution of about 0.2% sodium hydroxide by weight and thenspraying the yarn with a weaker sodium hydroxide water solution of 0.02%sodium hydroxide by weight strength. In the second stage, thetemperature of the liquid spray was also 30° C. to obtain a slightlybasic yarn.

In a first treatment stage, the yarns were partially dried on a pair ofsteam-heated rolls at a first average temperature (TEMP 1) under a firsttreatment tension (TENSION 1) for a first roll contact time (TIME 1)resulting in the yarn having a moisture content of at least 30 wt %based on the weight of the dried yarn.

Without further drying, these “wet” or “moist” yarns (called “neverdried yarns”) were then fed into a second stage. The second stagecomprised six hot rolls maintained at an second average temperature(TEMP 2) for a second roll contact time (TIME 2). The fiber wasmaintained at a second treatment tension (TENSION 2) in this secondstage.

The yarn passed from the second stage into a third heat-treatment stage.The third stage comprised eight hot rolls maintained at an third averagetemperature (TEMP 3) and the yarn contacted these rolls for a third rollcontact time (TIME 3) while the yarn was under a third treatment tension(TENSION 3). A Raytek model 4WA67 infrared temperature measuring unitwas used to record all roll temperatures.

Then for all examples, except example D, the yarn passed into a fourthtreatment stage, a “cooling” stage, comprised of a plurality rolls at150° C. that reduced the yarn temperature to 150° C. prior toapplication of finish or subsequent water treatment. In example D,finish was applied before cooling.

The yarn was then passed through finishing and water applicators andfinally wound onto a spool into a package. The oil from the finishingapplicator provides surface protection and lubrication properties whilethe water applicator provided 4-8 wt % moisture for yarn stability andstatic minimization.

Extruding and washing process conditions for all runs are shown inTable 1. Yarn treating process conditions for all runs are shown inTable 2. Cooling and finishing process conditions for all runs are shownin Table 3. Final wound yarn properties for all runs are shown in Table4.

For each comparative example and each example illustrating theinvention, the final yarn properties shown in Table 4 were determined bytaking multiple yarn samples from multiple spools of wound yarn. First,the values for the samples from the same spool were averaged. Then theaverage of these spool averages is reported in Table 4. For example 1,five yarn samples were tested from each of 12 spools. For example 2,five yarn samples were tested from each of 16 spools.

TABLE 1 EXTRUDING AND WASHING PROCESS CONDITIONS Percent aqueous PolymerDiameter sulfuric Line Line Polymer wt % in Spinning D1 - of Coag acidfor Time in Speed Speed Inherent Spinning Solution Air # of SpinningNumber of Bath Co- Coag through through Viscosity Solution Temp GapHoles per Holes Spinnerets Temp agulation Bath Wash Wash Example (dl/g)(%) (° C.) (mm) Spinneret (mm) per Yarn (° C.) Bath (%) (sec) (m/min)(m/min) A 5.4-5.6 19.5 76 9.5 1333 0.064 1 3 7 0.023 457 457 B 5.4-5.619.5 76 5.8 1000 0.064 1 3 7 0.021 503 503 C 5.4-5.6 19.5 76 5.8 10000.064 1 3 7 0.015 686 686 D 5.4-5.6 19.5 76 9.5 1333 0.064 1 3 7 0.024434 434 1 5.4-5.6 19.5 76 9.5 1000 0.064 2 3 7 0.025 412 412 2 5.4-5.619.5 76 9.5 1000 0.064 2 3 7 0.025 412 412

TABLE 2 YARN TREATING PROCESS CONDITIONS Moisture Content Moisture TEMP1 - TIME 1 - based on TEMP 2 - Content Average TENSION 1 - Contactweight Average TENSION 2 - based on Temp of Tension Time of after Tempof Tension Contact weight Average Tension Contact Steam at Steam SteamSteam 6 Hot at 6 Hot Time of 6 after 6 Temp of 8 at 8 Hot Time of 8Rolls Rolls Rolls Rolls Rolls Rolls Hot Rolls Hot Rolls Hot Rolls RollsHot Rolls Example (° C.) (g/dtex) (sec) (%) (° C.) (g/dtex) (sec) (%) (°C.) (g/dtex) (sec) A 214 1.71 3.24 ≦15 280 2.16 0.32 <15 330 2.70 0.42 B216 1.80 3.30 ≦15 250 2.07 0.29 <15 315 2.34 0.38 C 216 1.80 2.16 ≦15250 2.07 0.21 <15 270 2.34 0.28 D 214 0.63 3.42 11 NA NA NA NA NA NA NA1 180 1.35 3.60 ≧30 260 1.35 0.35 >15 330 2.88 0.47 2 180 1.35 3.60 ≧30260 1.35 0.35 >15 330 2.88 0.47

TABLE 3 COOLING AND FINISHING PROCESS CONDITIONS Water Average Tensionat Contact weight percent Temperature of Cooling Time of after waterCooling Rolls Rolls Cooling Rolls applicator Example (° C.) (g/dtex)(sec) (%) A 150 1.5 0.42 4.0 B 150 1.5 0.38 4.5 C 150 1.5 0.28 4.0 D N/AN/A N/A 11.0  1 150 1.5 0.47 3.5-4.0 2 150 1.5 0.47 3.5-4.0

TABLE 4 FINAL YARN PROPERTIES Fiber Fiber Final Final Apparent ApparentFiber Fiber Yarn Final Final Yarn Final Fiber Crystallite CrystalliteCrystal Linear Linear Yarn Elongation Yarn Orientation Size SizePerfection Density Density Tenacity to Break Modulus Angle at 110 PeakAt 200 Peak Index Example (dtex/f) (dtex) (g/dtex) (%) (g/dtex)(degrees) (Angstroms) (Angstroms) (%) A 2.5.0 3155 19.7 2.38 796 8.2 6853 54 B 1.67 1578 21.7 2.45 837 8.0-10.0 55 51 53 C 1.67 1578 20.4 2.55765 8.0-10.0 55 51 53 D 2.25 3333 20.6 3.60 513 16.0  46 45 42 1 1.573123 21.7 2.55 850 7.0 73 54 55 2 1.58 3150 20.6 2.37 860 7.3 76 58 61

In summary, Table 4 shows that only inventive examples 1 and 2 resultedin a yarn have a linear density of at least 2650 dtex and a modulus ofat least 810 dtex. Further, Table 4 shows that only inventive examples 1and 2 resulted in a yarn with fibers having an orientation angle of nomore than 8 degrees.

Comparative Example A shows that a yarn was produced with a yarn lineardensity greater than 3155 dtex with a tenacity of at least 19.7 gramsper dtex and an elongation to break of at least 2.38%. However, it didnot have a modulus of at least 810 grams per dtex.

Comparative Example B shows that a yarn was produced with a tenacity ofat least 21.7 grams per dtex, an elongation to break of at least 2.45%and a modulus of at least 837 grams per dtex. However, it did not have ayarn linear density greater than 1578 dtex.

Comparative Example C shows that a yarn was produced with a tenacity ofat least 20.4 grams per dtex and an elongation to break of at least2.55%. However, it did not have a yarn linear density greater than 1578dtex or a modulus of at least 810 grams per dtex.

Comparative Example D shows that a yarn was produced, without thetreatment or cooling stages, with a yarn linear density greater than3300 dtex, a tenacity of at least 20.6 grams per dtex and an elongationto break of at least 3.60%. However, it did not have or a modulus of atleast 810 grams per dtex.

Those skilled in the art, having the benefit of the teachings of thepresent invention as hereinabove set forth, can effect numerousmodifications thereto. These modifications are to be construed as beingencompassed within the scope of the present invention as set forth inthe appended claims.

What is claimed is:
 1. A yarn, comprising: (a) a plurality of fibershaving an orientation angle of no more than 8.0 degrees and made ofpara-aramid, (b) a linear density of at least 2666 dtex (2400 denier),(c) a modulus of at least 810 grams per dtex (900 grams per denier), and(d) a tenacity of at least 18 grams per dtex (20 grams per denier). 2.The yarn of claim 1, wherein there are 1100 to 2500 of the plurality offibers and the fibers have a linear density of 1.10 to 2.50 dtex (1.00to 2.25 denier).
 3. The yarn of claim 1, wherein the para-aramid ispoly(p-phenylene terephthalamide).
 4. The yarn of claim 1, wherein theyarn has a linear density of 2666 to 3444 dtex (2400 to 3100 denier). 5.The yarn of claim 1, wherein the modulus is from 810 to 990 grams perdtex (900 to 1100 grams per denier).
 6. The yarn of claim 1, wherein thetenacity is from 18 to 25 grams per dtex (20 to 28 grams per denier). 7.The yarn of claim 1, wherein the orientation angle is 5.0 to 8.0degrees.
 8. The yarn of claim 1, further comprising the fibers having anapparent crystallite size at the 110 intensity peak of 70 to 85Angstroms.
 9. The yarn of claim 1, further comprising the fibers havinga crystal perfection index of 55 to 70 percent.
 10. A continuous processfor making a para-aramid yarn having a linear density of at least 2666dtex (2400 denier), a modulus of at least 810 grams per dtex (900 gramsper denier) and a tenacity of at least 18 grams per dtex (20 grams perdenier), comprising: extruding an anisotropic solution of para-aramid ina solvent-through a spinneret having a plurality of holes forming aplurality of fibers, passing the fibers through a gas and then acoagulating liquid, combining the fibers into a yarn, washing the yarnwith a washing solution, removing some of the washing solution from thesurface of the yarn, treating the yarn by heating the yarn from 120° C.to 260° C. under a tension of 0.90 to 2.25 grams per dtex (1.00 to 2.50grams per denier) for a first heating time of 1.6 to 6.0 seconds, andafter the first treating step, treating the heated yarn from 300° C. to400° C. under a tension of 2.25 to 4.50 grams per dtex (2.50 to 5.00grams per denier) for a second heating time of 0.2 to 5.0 seconds,cooling the yarn to a temperature of 125 to 170° C., applying a finishon the yarn, and winding the yarn on a spool for the first time in theprocess.
 11. The process of claim 10, wherein the yarn further has alinear density of 2666 to 3444 dtex (2400 to 3100 denier) and the fibershave an orientation angle of 5.0 to 7.5 degrees.
 12. The process ofclaim 11, wherein the yarn further comprises the fibers having anapparent crystallite size at the 110 intensity peak of 70 to 85Angstroms and a crystal perfection index of 55 to 70 percent.
 13. Theprocess of claim 10, wherein the para-aramid is poly(p-phenyleneterephthalamide).
 14. The process of claim 10, wherein in the firsttreating step, the yarn is heated from 150° C. to 200° C. for the firstheating time.
 15. The process of claim 10, wherein in the secondtreating step, the yarn is heated from 340° C. to 380° C. for the secondheating time.
 16. The process of claim 10, wherein in the first treatingstep, the yarn is heated in a first oven section or by a first pluralityof hot rolls and in the second treating step, the yarn is heated in asecond oven section or by a second plurality of hot rolls.
 17. Theprocess of claim 10, wherein in the first treating step, the yarn isheated by a first plurality of hot rolls and the time that the yarncontacts the hot rolls is the first heating time.
 18. The process ofclaim 17, wherein the first plurality of hot rolls includes at least twosteam heated rolls and the yarn contacts the steam heated rolls toremove most of the wash solution from the yarn.
 19. The process of claim18, wherein the first plurality of hot rolls includes a first pluralityof electrically heated rolls and the yarn contacts the at least twosteam heated rolls before the yarn contacts the electrically heatedrolls.
 20. The process of claim 17, wherein in the second treating step,the yarn is heated by passing the wet fibers over a second plurality ofhot rolls heated and the time the yarn contacts the rolls is the secondheating time.
 21. The process of claim 20, wherein the second pluralityof hot rolls are electrically heated.